Most cell membranes communicate with extracellular environment by means of receptor and channel proteins located within the cell membrane. Receptor and ion channel proteins can be gated by molecules which bind to the receptor and signal the binding event by opening the ion channels through which ions such as sodium and chloride ions can flow. Ion channels can also be gated by the cross membrane potentials through the voltage sensor components in the protein molecules. Like modulators of receptors, the levels of cross membrane potential can regulate such voltage-gated ion channel activities, generating most of the neuronal and muscular activities. Ionic flux across a cell membrane generates electrical current that can be measured with appropriate recording equipment. Such electrophysiological studies of receptor and ion channel function often utilize unfertilized eggs, or oocytes, taken from the South African clawed frog, Xenopus laevis. Xenopus oocytes have the ability to synthesize functional proteins when microinjected with exogenous mRNA or cDNA constructs.
In electrophysiological analysis, an oocyte is electrically connected to intracellular voltage and current measuring and clamping devices. FIG. 1A shows a side view of a prior art recording chamber 2 that accommodates an oocyte 3 immersed in a solution 4. A voltage electrode 9 and a current electrode 9 are held by manipulators 6 and positioned so as to contact the oocyte to measure intracellular voltage and current signals. Two ground electrodes 7 and 11 are coupled to the solution in the recording chamber by agar bridges 8. The oocyte's response to the solution may be measured by maintaining a constant voltage between voltage electrode 6 and ground electrode 7, and measuring the current changes flowing through current electrode 9 and ground electrode 11. FIG. 1B shows a top view of recording chamber 2, which is connected to a multi-barrel manifold 124 through an inlet 120. Manifold 124 allows different solutions to be diffused to recording chamber 2. An outlet 122 connected to a suction pump (not shown) allows solution 4 to flow out of recording chamber 2.